Cuda SRT8 392 Gen.III Hemi

Here's the current status of my Cuda's body. All body work and mods are completed. I've since removed all the glass from the car and taken the doors off. It is literally ready for the final scuff, coat of sealer and the paint. I do want to determine what type of coating I'm going to use on the underside. I want to spray it on prior to painting the top side. I don't care for body color down there and am looking for just the right brand of a very fine texture, thin, spray on urethane undercoat.